Inkjet printers eject drops of ink through very small openings, sometimes called nozzles, on to a print medium. Each drop forms a dot, sometimes called a pixel, on the media. Printed images are formed from many such pixels. Ink ejection nozzles that are not used frequently may become clogged as liquid evaporates from ink in the nozzles or from ink lying on the upstream side of the nozzles. Ink drops cannot be ejected through clogged nozzles. Hence, it is desirable to unclog a nozzle before using the nozzle to print a pixel.